This invention relates generally to control circuits and particularly to such a circuit for controlling a system for supplying ink to an intaglio printing device.
Intaglio printing is a technique of printing bar codes on nonporous objects and is well known in the art. Typically in such printing, a smooth inking surface contains a substantially rectangular aperture. A plurality of substantially flat inking bars are stacked together and are arranged along one dimension of the aperture such that the combined thickness of the bars substantially fill the aperture. The inking bars include an inking edge which spans the other dimension of the aperture such that the inking edges substantially fill the other aperture dimension. The inking bars have a thickness which is determined by the desired width of the bars in the bar code to be printed. The entire inking surface, including the inking edges of the bars, are covered with ink by a mechanical member which drags ink from a reservoir across the inking surface. A squeegee-like scraper member is used to remove ink from the inking surface. Prior to inking the inking surface, selected inking bars are depressed to lie a small distance below the inking surface to form cavities between the nondepressed bars. Ink fills the cavities and remains in the cavities after the ink is removed from the inking surface. A nonporous, resilient member is depressed against the inking bars and enters the cavities to transfer the ink from the cavities to the resilient member. The resilient member is removed from the inking surface and brought into contact with the object upon which the bar code is to be printed to effect the transfer of the ink from the resilient member to the item to be identified.
In intaglio printing devices of the type described above, ink is applied to the inking surface and the inking bars by pulling an ink spreader through a reservoir of the ink which is immediately adjacent to the inking surface. The ink is thus spread over the entire inking surface as well as the inking edges of the bars. Subsequently an ink scraper removes ink from the inking surface and from the inking edges of the printing bars leaving ink in the depressions formed between the nondepressed inking bars. In instances when the ink supply in the reservoir becomes low, the ink is not uniformly applied and voids can exist in the ink on the inking surface, or on the inking edges of the bars. In such instance inaccurate codes can be printed on the object. Accordingly, there is a need for a system for detecting the need for raising the level of ink in the inking reservoir while simultaneously avoiding overfilling the ink reservoir. The present invention fulfills these needs.